The proposed research is part of a continuing effort to map nonhuman primate social cognition. It marks a shift in PI's methodology from observation of spontaneous behavior to noninvasive experimental manipulation. The aspect selected for study is social reciprocity, which is considered a key element of human social functioning and morality. A previous study of captive chimpanzees (Pan troglodytes) suggested food- sharing as a promising dependent variable in this species. An outdoor-housed group of captive chimpanzees will be subjected to food trials in which all individuals are present, as well as to experiments designed to increase the optimal character of food sharing. This will be achieved by temporary separation of particular individuals during which time they will discover food and subsequently be given the choice to either rejoin the group or consume the food undisturbed. In a variation on this experiment, subjects can consume the food on their own but conspecifics will be allowed to watch. A comparison of behavior across the various conditions will test the prediction that chimpanzees take the perceptions of conspecifics into account. Because of the close taxonomic relation between humans and chimpanzees, the reciprocity system of chimpanzees may depend on emotions, social pressures, and cognitive evaluations that are fundamentally similar to those underlying human reciprocity. Investigation of how individuals judge and influence one another may increase understanding of misjudgments underlying social dysfunction.